346 FOOD SCIENCE APPLICATIONS 



small amounts of iron. Other metals and phosphorus are present in small 

 amounts in some specialized types of proteins. 



The approximate amino acid composition of fish proteins is very similar 

 to the composition of mammalian flesh; hence consuming of fish proteins 

 represents an eflficient way to supply the amino acid requirements of 

 man and other animals. In particular, it is necessary to furnish those 

 amino acids which cannot be synthesized by the animal organisms. These 

 "essential" amino acids occur in abundance in fish. 



Lipids. Fish body oils are composed primarily of triglycerides which 

 differ from those of animal and vegetable origin in two ways. Whereas 

 animal and vegetable oils contain only very small quantities of fatty acids 

 having more than 18 carbon atoms, the chain length of as much as y^ of 

 the fatty acids of fish body oils exceeds this value. Most of these long 

 chain fatty acids of fish oils consists of C20 and C22 fatty acids. Very 

 small amounts of C24 fatty acids occur in some oils. The fatty acids of 

 fish oils also contain more double bonds than is the case with animal and 

 vegetable oils. Thus a large part of the C20 fatty acids of fish oils is a 

 pentaene (five double bonds) and a large part of the C22 fatty acids is a 

 hexaene (six double bonds). Vegetable and animal oils contain almost no 

 pentaenes or hexaenes. 



In spite of the high content of these polyunsaturated fatty acids in 

 fish oils, the content of the classical essential fatty acids, linoleic, linolenic, 

 and arachadonic acids, is relatively low as compared to the content of 

 these acids in oils from animal or vegetable sources. Although fish oils 

 are low in these classical essential fatty acids, evidence available would 

 indicate that most of the polyunsaturated fatty acids of fish oils, while 

 unable to cure dermal symptoms such as linoleic and arachadonic acids 

 will do, are members of the linolenic acid family (first double bond at the 

 three position counting from the terminal methyl group end) and, as such, 

 will adequately support growth. 



The depot fats of fish consist primarily of triglycerides. Much of the 

 lipid associated with the cells of the flesh occurs in non-triglyceride forms. 

 In some species of fish such as haddock and cod, where the amount of 

 total lipid content in the flesh is of the order of 0.6 per cent, the vast 

 majority of the lipids occur as phospholipid and in other non-glyceride 

 forms. Thus Olley and Lovern"* report the lipids of haddock flesh to con- 

 sist of lecithin, 42.8 per cent; unidentified lipids, 15.2 per cent; waxes 

 and alcohols, 10.5 per cent; free cholesterol, 6.1 per cent; free fatty acids, 

 6.1 per cent; phosphatidylethanolamine, 5.4 per cent; inositol lipids, 

 4.4 per cent; cholesterol esters, 3.4 per cent; triglycerides, 2.4 per cent; 

 hydrocarbons, etc., 2.0 per cent; and plasmalogens, 1.7 per cent. Olcott, 

 et al}, have reported that the phospholipids of albacore tuna consist of 

 about 65 per cent phospatidyl choline, 25 per cent phosphatidyl ethanol- 



